We have developed a computer program to guide the physician in the use of digitalis glycosides in the medical therapy for congestive failure in the common arrythmias. The program embodies principles gleaned from the study of the way in which experienced cardiologists deal with digitalis. The program uses a patient-specific model to determine dosage and it uses feedback information about a variety of clinical aspects of the patient's response to therapy to modify its recommendations. The patient-specific model incorporates knowledge of the pharmacokinetics of the drug as well as of those special features of the patient's condition that may alter his response to therapy. Although the program uses serum levels of the drug when they are available, it does not require them, and instead it relies principally on the clinical manifestations of the drug and the patient to assess therapeutic and toxic effects. We are proposing here to conduct a one year evaluation of this program. In this trial, the program will be challenged with a 100-150 cases of digitalis administration from the Veterans Administration Hospital in Houston, and its decisions will be compared with those of the clinicians actually managing these cases. A panel of experienced cardiologists will judge the extent to which the program's performance equals that of the attending clinicians. The magnitude of the problem of digitalis toxicity is considerable, because although most dangerous procedures in the practice of medicine are undertaken by experts, digitalis is administered by cardiologists, internists, and general practitioners alike. If our program can be shown to make sound clinical decisions regarding digitalis administration, then it represents a form of distributable expertise which can be made available widely to help physicians. The evaluation we propose here is a first step toward that end.